Sound-signaling device



1,563,626 H. HECHT ET AL `SOUND SIGNALING DEVICE Filed Jan 5. 1921 e sheets-sheet z Dec. 1, 1925 I Dec- 1.191251? l" V H. HEcH'r- ET AL. y l SOUND SIGIQALIBIGV DEVICE 4 Filed Jan. 5, 1921l 5 'sheds-#sheet 5'- I fPaitentedDec. f

'g-To all whmn t may coment.

vrlaiiusrofrnn;1omarmt.seinemM 111,01; grmiggwnygj f.

AVILHELM fR'vponru," lH'U'oo Q LICHTE, and 'u "WALTER HAHNEMANN;'citizens' Vof 'the Grer-v man Republigand J Yresiding at- Kiel, at-Y'Kiel," u atv Kiel, yand at Kitzberg, near Kiel, county@` j ofl Schleswig-Holstein, State of-y Prus'simf "l have invented certain ,nevand usefulflrnf1 v *proveniente* sin SouvndSignalin'g Devices (fori which we-'havej'filed' applications' in' Germ any on Ma rch 10th,'v 1917 October 6th,V 'A l 19-17, :November 5th,-1917,?j'November 14th,); '1917,' January 6th,'.1919,`July August 6th, 1919,and 'Augi`1st`20th,y 191,9;` 'in .Denmark on .September 25th, 191-9 ;t in Nor-f Way -on October Y10th, 1919;in Sweden on" October 16th, 1919; -in-Holland on Novem i j berf29th, f1919;5infBelgiuxn onQfJulyjfSth, :1920;v in France'on'.luly`-8tl1, 1920; in Ivtaly'fv on'fJ'uly 9th, V1920;Y in'jEngl-andonluly 9th," 19201and July 10th, 1920;'inSpain on ulyj 10th, 1920, No. 7,4648'gla'nd Vin JapanonJuly f 10th, 1920), ,off which ,the @Hering is -a specification;

' The present invention relates u;v signaling,

devices for sending orY receiving sound-sig? A Y V-'I' on the other hand the radiating surface i nals throlglghWater; and injwhelit'he sound Qian:

' ceiving electric Wavesvibrations; are transferred from a lsurface 'fabuttingf against the 'sound propaga-ting,-v liquid orlm'ediiu'n to zthev receiving dex'ricel 1 "proper, or .torthersaid surfacel fromH alsoundproducing' or sendingfvde'vic'e, by means of a, g sound"transferring or' coupling i'zharnbery @filled Vwith-a highly ycompres'sible 'medium' @was` such' as a gas.l

l VWhen receivingl signals fromthe`o\1ter Waterfthe surface abutting against the'Waterv does-not absorb yor pass onall of the sound vibrations impinginguponv it but reflects 'or radiates bac-ka certain amount of the sound.. Hence this surface will beatermed'the radii' atingysurface orfmem'ber both wvliensig-f '-'fnals are receivediby it sentout from it.v

vaerial wire,'orfairjwire. 1 A f l "Apparatus having asound"transferringY or coupling chamber arranged betweenthe y ',fjkkradiating member and thesOund receiver or Vproducer-'iroper are-known, butkthey have' 2 ainountofnsoundener v transferredbyithe jradIat-ngsurace eit er from or zoythejjA 31std ,1919;

1, length of the; sundpropagated'. en; dei

'ef 'vibration' fer. medlum :mdl

` heretofore "it `vv'illfbe found' that the` above consi,derationsv have vplayed no fpert. -Y The couplingt chambersV that contain*fthe lsound and ivlienftlieyfalfe Y Vthat'forni :the-'sound -transforungi"member-` The conditions existinfrliere are analogous: tofthose'in Wireless telreg'raphywliere thief :aerial structure that is'usedgboth for radiate. ing or sendingout and-for absorbing orre! calleclan antennaff Y v f' *I-'ffsion even if, in-'accordanoezfwith 'proposals sult's Off'af'precticalj'valnefto be obtained; A The.: reasol'lfjo'f.` this ist the .following :l-The water vis defined by theixtenttofwhich 'existl for a Vgiven' radiating surface. f If-jthe- 'IIS` Vnatural periodic'tirn' ot the radiatingfs'uri Y face isr not'A made to con/form ,tov the `f requex'icy' to'an extent thatcorres'ponds to theehange` s v of volume of the sound-'propagating medium; `80

'ways remainV Within certain liinits, th'ea'mv4 i V i Y y pltude of themotionfexecuted bythis surface is alwaysgcornparableto thatofffthei between'thegradifating surfaceand'tlieaotu'al v receiving or sound'` prodvcing devlcea-re al- 100 abovereniarksgwill be found to be muehtoo large to obtain aneiicient ysound transnns-fy `that have also already',beenmadeytliegfen-f'M145V s j A* closed Ygas is ke t'underpressurefbeceusgj on accountof tlie largensizeof'thejfsound transferring'chambers `proposed, this*-pres-`Y sure would have to be `far too high for-prac.-

.ithan those heretofore reduc tical purposes.

The object. of the 'resent invention is to provide sound signa in a paratus of 'the ind mentioned, ut o a `iher eclency This is accomplishe by. making the sound transferring chamber that contains a compressible sound conducting mediumv very small and shallow so as to convert it into an etlicacious coupling chamber. The Vterm very small means in this case that for a radiating member of average size the volume of the chamber shall amount to about only one or not much more than onecubicv centimeter, such a volume beingsuitable for instance in a case where sound vibrations are to be transferred from water to the diaphragm Yof a micro honic transmitter through a radiating surface and a chamber containing the compressible sound conducting medium, and where the coupling between `v the radiating surface and the microphonic transmitter is to be tight or close. f

With reference tofthe size of the cou ling chamber it may be assumed, as a ru e, that the ratio between its volume and the volume of the sound pro agating fluid mass abutting against the ra iating surface and oscillatinor in phase in all its arts must be so that the same, or nearly t e same, luc-' tuations of pressure may be caused to exist before and behind the radiating diaphragm.

In the case of a circular radiating surface ordiaphragm an eliicacious coupling chamber will be obtained if its volume is such as to satisfy the equation If a looser coupling is desired the coupling chamber must be made correspondmgly larger, but even then it wouldA not as a rule be advisable to go beyond an amount of a few cubic centimeters. Thus a means is furnished for adjusting the tightness of the coupling. Y

Anot er very simple means for regulatiiw the eliciency of the coupling agency, whic i the provision of a coupling chamber dimensioned in accordance with the invention will render more successful, consists in apply- Lacasse ing more-or le pressure to the enclosed gas.

able the pressure waves of the sound to pass through the' chamber to the other parts of the sound signalin apparatus, such as a sound conductor w ich conducts the sound to an operators station, it Ais preferably closed to these parts by a diaphragm that is adapted for executing suitable vibrations.

The smallness of the coupling chamber greatly increases the effect of the pressure which need only be small, or changed, in a small degree, in order to produce an appreciable tightening of the coupling or vice versa.

Hence if a higher pressure is applied in the coupling chamber a coupling can be obtained with a somewhat larger chamber that is just as good as the `coupling produced at a low pressure with a very small chamber.V

From this thegeneral rule ,may be deduced that during operation the quantity of the enclosed gas per unit of space must always be such that a close coupling is obtained between the radiating member or diaphragm and the parts of the sound signaling aparatus to which the sound is to be transerred, i. e. the actual sound producer or receiver or the sound conductors leading to the roducer or receiver.

Tie understanding of the invention is lightened by the following explanation: As said in the foregoing paragraphs two spaces at the two faces of the radiatin diaphragm are of interest, one of them be ore the diaphragm being filled with water and having an extent of a radius of about half a wave length of the propagated frequency, the other behind the diaphragm being filled with air and inserted between the diaphragm and the sound leading devices. Then sound strikes the diaphragm the waterlilledspace contains a definite amount of sound energy in the form of oscillations of the molecular 1 parts of Water, the variations of pressure at the face of the diaphragm being compa-ratively great in comparison with the extent of these oscillations. For transferring the same amount of energy into a normal air illed chamber it would bc necessary to change both components of energy i. e. to enhance the amplitudes of motion and to diminish the amplitudes of pressure, becausel the compressibility of air is very much greater than that of water.'

As stated in the earlier paragraphs oi" this application the motions of the radiating diaphragm are limited by the extent of the motions of the Water. Thus the volume of Van air filled chamber according to the present invention is varied by the definite oscillatiQDS 0f the diaphragm within a definite i151` Inaccordance.withf'this explanatio'nthe rate, and the smaller theairf volume in 'such a. chamber isma-de the greater the pressure VVariations grow. In vthis Way it ispossible to obtain substantially equal pressure Variai 5 vtions `iniboth thel spaces before andfbehind inthis case both media, the Waterk and the 1o' fin consequence of itslittle compressiliility,

theflatter inY consequence. of thel smallness o flit's .volume with relationto 'ther portion ot1the-radiating. member acting thereon-rior osci lationsper second, the couplingchamacted upon.

Ainvent-ion'can preciselyrbef defined bysaying: For transferringa sufficient amount of sound-energ* from thewater tothe sound leading devices the volume of air in the chamber behind' the diaphragm must `rhave such a rsize that'the 4variations, of pressure Y l offthisair' become-equaloraboutlequalito.

` the'fpressure 'variations inthel water space before 1 the diaphragm, Vor in other words,` -gbothgfspaces must haver the same: Sound hardness. u y Y v- Y p' .The actual receivingfor.sound producing devicesthemselves inay in alll cases be combined vwith special timing strnctnreszqjor they Vmayv themselves! representsuch strnctures, or they may be made'fso as not to execute any natural. vi bratio ns. Similarlyfthe radiating surface mavlielmade to form a pa-rt ot' a ltiming structure, or it may itself represent antattnned"structnre,"'or be made so as not to execute anyim-tural vi/lgiration's. The entire apparatus'niay comprise-'two diaphragms", one Aof which represents'the-radiating surface abutting-vagainst'A the'sonnd l ui conducting liquid-whilst tliei'o'ther as associatedfavith the receivingor sound producing-deviceproper; and tlielelasticjforces of 4thesetwo diaphragms, and if desirable `thesev forces together with those- Of nelghbourineY i lmasses ofr llquld and gas, may be regulated with respect vto each; other `in -sucli a manner. that the. aggregate. vibrating lparts have only om` predominant'natural period' of vibration, or the; attuning ofthe parts may be 'asuch that the said aggregation 'of parts have twoqor morofrequencies on acconnt-oftwooi' fnioreparts .of different natural rates yof vi- Y bration. beingcoupled to eachother. Another fli-atinc of the invention consists :iin an vvarrangenlent' of. the couplingv chamber which1 the cilicacy ofthe couplingis :less

, fat vfreqnencies that are higheroit-lower thanl the chosenV operatingire'quency, so that4`v 1f y1t ia assumed that the 'apparatus under 'consid- 'rol eration isa recei'velz only 'the sound Yvibra- @tions lying 'Within acertain range ofifref q'uencie'snillvbe received,th`is result being' obtained'in the first placemerely throi'xgh Vthe ar 'angement .ofthe chamber itself WithyCTV-'ont any'additional aidbvfa. tuning voifjtlie members-of `the apparatus. This is accom#v plishedin thefollowing manner:

It ,has been Yexplained `above that, assum-Y ine ythegcouplings to be the same, Vfthe volume ofthe water near the radiating rsur.- `70 face, Whose parts.- vibrate A'in .phajse with each other, i.V e. the volume which istofbe? taken into account invdetermining'thevohune offthe coupling chan'ibeig.decreases as the third-power of the-Wavey length.VV

j Hence if thopropoi'tions of the coupling chamber have been determined forafcertain i `cou. ling 'effect ata frequenc-yof;sayiQOO() b erfwillbe too large for higher frequencies, 80 `\i. e. for sinallerxvave lengths, and everyin-j ,i

crease of the periodicity-will be kautomaticallyaccompanied by a corresponding/loos! Y ening "of `the coupling. If it is desired Sto i cause the 'tightnessA of the coupling to alec)V` vfalloft' when the fre u ency is lowered-this may.y be accomplishedli pling ohamberathrough a, passage that eXf ertsia ce1 tain throttlinge'ect onithelgas to .Some other .elastic-inedium,fand by' cansf ing the throtthng action to besuch thatit. 1s very effective Yat .the chosenv 'periodicity of v say;2000,.but falls oi rapidly when thepe-v i5' The resulty of thisfar, 95" l rangement 1s that-,'as-'far as the lo'n'cr ffreriodicity@decreases.v

quencies are concerned, .the volume that de- A i termines the-coupling' effect ie the volnnjie off the coupling chamber addedjtothatvjof'the 'second chaniber,and ifthese-chainbers are I100.r

properly diniensioned-v,g` the lower `tliefrclquency is, thelooser the;couplingfjwillA be.- 1t followsy fr'oni'itheVabovogthat withv an given coupling chamberitlie ytightne alor, "closeness of the coupling `effected `by`it del creases, andv a similar decrease offgtlie con;

viciently narrow. passageVY at .through :rffsuit able throttling `device toi the -aforesaid sec i.

ance with 'the .invention thc ad uSitinents-'tlurt may.thusbe'eIfectcd by changing the' sizeof' I the coupling chamber; or "alternating the..

efficiency of the. tlnot'tling device Y situatedv l between thecouplingchamber and the s'ecj- V12 if ondj auxiliarychamber,may be executedinf loco onwithtlie of"distant, control'de An importantfeature consist'si'nthe means itjafords forreg'uy.125e

lating within Wide limits therratio oftra'nfsf formation between the amplitudes of VUthe( oscillations tliattakeV place at the radiating surface Y. and the correspond ingv amplitudes" Y at the Vsound producing. `vdevice 'on receivingV 71370',

yj connectingfthe-cou 7 -a second largerchamber filled YWith air or 9e 10 creases many CaSeWhenthe ire'qi'itmy-iin-1.` f v plinglrerl'ect i na`y;bcy obtained byfco V necting- V Y the cou linffchamber )ro )erthrou rli a 'Sub l n Y. Y in `"produced between the gas set `in motion by the sound radiator and the walls of the chamber is considerable, especially in chambers of a conical shape because, Von account of the high compressibility of the medium with which the chamber. is lled, the par ticles of the medium execute in addition to Vthe desired axial movements also very large transverse movements. A preferred means for reducing this friction consists in filling the chamber with a combined charge comprising a practically incompressible medium (liquids) and a highly compressible medium (gases), the vlatter being placed in Va special vessel of such a form that as large a surface .as possible is presented to the incompressible medium and that the particles of the highly compressible medium execute oscillations in a direction that is in general vertical to the said surface. Y

Another improved means of reducing the said friction that may be employed either in apparatus charged entirely with a com pressible medium, or in such as are charged with a combination of compressible and incompressible media, consists in establishing the coupling by means of gases that produce little internal friction, as for example'hydrogen, ammoniac or the like. This expedient offers the advantage that it renders it possible to operate with the smallest possible damping (smallest loss) at the outset. If it then turns out that a greater damping effect is required (sayfor the purpose of broadening the crest of the resonance curve) this can be done by first increasing the useful damping, as by extracting energyby a detector in receiving signals, and by then introducing any desired amount of damping that might still be wanting to bring the total damping effect up to the desired figure. This procedure may be adopted for example whenever in apparatus serving for the transmission of signals the tuning becomes too sharp for reliable operation. or when in apparatus intended for the detection of noises a disturbing distortion of these noises i occurs through the natural vibrations that are set up in the apparatus itself being insufficiently damped.

In accordance vwith the invention the damping yof apparatus may be'increased when desired by increasing the useful damping by providing specialdamping means in the cou ling chamber or at its confines, which a Sorb a part of the energy of vibration in the said chamber.- In addition toa number of known damping means the fol lowing means may be advantageously employed. The walls of the coupling chamber may be entirely or partly made of yielding substances in which a large amount of internal friction is produced. In cases where the construction of the apparatus is such as to render the use of such walls impossible they may be entirely or partly lined with the said substances. Other kinds of damping means that may be employed are grids, netting or porous partitions inserted in the couplingI chamber in such a manner as to exert a throttling effect on the enclosed medium that is set in motion by the radiator.

The application of damping means aforesaid is of course not limited to apparatus in which the coupling chamber is closed to the passages leading away from the chamber to other internal portions of the apparatus, for this means may be advantageously employed in all manner of apparatus, no matter how the energy is caused to pass from the internal parts of the apparatus into the coupling chamber, or out of this chamber into the said internal parts.

Other important features of the invention, which, in addition to those mentioned above, appear in the appended claims, will be more readily understood when described by reference to the accompanying drawings in which various embodiments of the invention are illustrated.

Figs. 1 to 3 are sectional representations of sound signaling apparatus with shallow, conical coupling chambers; the apparatus of Fig. 1 having its coupling chamber connected to a'large auxiliary chamber by aV channel containing a throttling member, the apparatus of Fig. 2 being Vprovided with a supplementary or third diaphragm, and the apparatus shewn in Fig. 3 being provided with a device that enables the coupling to be changedwhilst the apparatus is in operation. r

Fig. 4 illustrates a section of an apparatus in which the coupling chamber is charged partly with gas and partly with a li uid.

Figs. 5 Vto 7 illustrate sections o sound signaling apparatus having special damping means arranged in their coupling chamf bers; this means consisting in Fig. 5 of a wall of yielding substance placed between the coupling chamber and an annular cavity, in Fig. 6 of a special lining on the interior wall of the coupling chamber, and in Fig. 7 of perforated or pervious partitions arranged in the coupling chamber.

Figs. VFi to 10 show sections of apparatus in which the coupling chamber is in communieation with a second gas chamber through a narrou7 opening; the second gas chamber consisting in Fig. 8 ofa sound con ducting tube leading to a soundproducing device, in Fig. 9 of a space that acts as a mout-h piece in a divers helmet and in Fig. 10 of a space in which an electrical sound detector is placed which converts the sound energy into electrical current fluctuations.

Figs. 11 tol are sections of apparatus in which the radiating member and the coupling chamber consistof independent parts that are operatively connected by an intermediate member; this memberconsisting in Fig. 11 of a piston Whose one end enters the coupling chamber and Whose other end is attached to the center of the radiating member, in Fig. 12 of` a piston arranged Similarly to that of Fig. 11 except that the v end adjacent to the coupling chamber is attached by a` soft vannular diaphragm yto the.

rear Wall of the casing, and in Fig. 13 of an oscillatory structure made up of two vibratelastic rod.

F1 g. 14 is a section through an apparatus in which the essential -part of the coupling chamber is a cylindrical space opposite to it does not come into account.

Fig. 15 represents a sectionv through a sound signaling box of an apparatus of capsular form in which the coupling chamber is attuncd so thatits acoustic properties stand in a certain relation to those of the diaphragm, preferably so, that the diaphragni and the coupling chamber have the 4o,- i

same pitch.

Fig. 16 shows the resonance curve of thel apparatus of Fig. 15.

v Fig. 17 illustrates a form of sound com-v ynuinicatiou apparatus in which the sound conducting tube is spaced from the Walls of the coupling chamber, and in Which the ,coupling chamber is provided with the means for varying its volume and the nor-l mal pressure therein' and with the gas throttle device.

Figs. 18 to 20 illustrate" various Ways of mounting sound boxes in accordance with y the invention; the manner illustrated vin Fig.

1S consisting in fixing the sound box in an aperture in the wall of a ship oi buoy, in Fig. 19 in providinga valve throughwhich the Water is sluit out from or admitted to the Sound box, and in Fig. 20 of a modification ofthe arrangement of Fig. 19. l i i Fig. 21 sheWs the apparatus of Fig. 18 mounted on the rear Wall of a Water-box attached tothe interior ofa ships hull, and

Fig. 22 illustrates a similar arrangement ing masses connected to each other by anship having sound signaling apparatus asv shewn in- Fig. 23 arranged in Water boxes attached to'opposite sides of the hull.

. Fig. l represents an electromagnetic device that maybe used either as a sound producer or a receiver and which is designed for operation under Water.

For conven- 'A ience of description it will be assumed that the device is a receiver, although it could also be used as a sender without lany fundamental alteration.v l is the radiating sur face that abuts against thev outer Water and is made in the form of aldiaphragm. Thisv diaphragm 1 closes the interior cavities of 'the disk-shaped casing against the 'outer water, the submerged casing: b en f made Water tight on all sides. The vchaniers inl side the casing are filled with `air.-f3 is a,y

secondary diaphragm that is arranged` opposite the primary' diaphragm 1. A flat coupling chamber `4 of very small-volume ,e

with respect to the area of theradiating sur` lface acting thereon or acted uponand 'filled with air is arranged between thetwo diaphragms, the volume of the chamber being made smaller the tighter the acousticcoupling between the diaphragms isto bef Fixed to the diaphragm' 3 is a svrnallyarma-v ture 5' placed opposite to the electromagnet- 6 which is attached -to afsmall cross-beam 'i' that is in turn fixed to the inner lWalls of the vessel or casing 2. The chamber 4 is connected with the larger part ofthe inner cavit 10 by a channel 8 in which therey isY provided a throttling member 9. If a tone of a frequency of, say 2000 vibrations per Second: is to be received from the Water, itz

Will be necessary, if the coupling is to' be a fairly tight or close one, and if the air in i the coupling chamber is kept ata normal pressure of onel atmosphere, to malte the size of the chamber 4 lessy than one cubic centimeter. VHence the distance between the -two diaphragms will, if their .diameters vmeasure say a few centimeters, not amount to more than a' few tenths of a millimeter. If the coupling is to be such that onlyla part of the pressure fluctuations of the coupling medium "are communicated to the diaphragm 3 this can be achieved either byv a corresponding enlargement ofv the coupling'y chamber or, in the case` of an air charge kept under pressure, by a corresponding reduction -of the pressure applied, or by connecting the coupling chamber 4 with the chamber 10 that is several times larger than f the chamber 4. If the last means is adopted lthe connecting passage must be made to exert the throttling effect required to obtain the desired tightness of coupling by the chamber 4. It has already been pointed out in the preceding statements that this throttlino' means has the advantage that its eflicacy diminishes as the frequency drops, so that the apparatus becomes less sensitive with decreasing frequencies. The explanation for this is that if the diaphragm 1 oscillates relatively slowly and thus gives rise to slow fluctuations of pressure in the chamber 4 a comparatively large quantity of air will have time to stream through the passage 8 into the large chamber 10 and the air that thus escapes from chamber 4 will not be available for bulging in the diaphragm 3. The larger the quantity of air 1s that is given time to escape from the chamber 4 the smaller the effect of the air on the diaphragm 3, i. e. the smaller the coupling effect will be.

Another advantage offered by the communicating passage between the chamber 4 and the space 10 is that it causes the diaphragm 3 to be relieved of the constant static pressure that would bear against it when the apparatus is submerged. When the apparatus is subjected to the ressure existing at a considerable depth t e diaphragm 1 is more or less bulged in. This would give rise to an excess of pressure in the chamber 4 which would be partieularl large on account of the extreme sma lness of the chamber and which would cause the dia- 36" phragm 3 with the armature 5 to be bulged in. This would mean a change of the distance between the armature 5 and its electromagnet 6 and an undesirable alteration of the sensitiveness of the apparatus. The

bers 4 and 10 by the channel 8 is that alterations of the static pressure do not cause the diaphragm 3 to be moved towards the cross beam 7.

In place of the electromagnet 5, 6 other forms of receiving devices such as a microphone that responds to pressure fluctuations or to a shaking action, or a tuned structure containing the receiving device as shown in the U. S. Patent 1,133,635 could be provided. If a microphone that responds to pressure fluctuations were employed the above described changes of distance would be deleterious.

Of course the diaphragm 3 may be relieved of static pressure in a known manner by arranging a third chamber and diaphragm in front of the others. The various members of the structures may also be attuned and dimensioned with respect to each other in a known manner and in such a way that the desired damping effect is produced. By selecting an adequate ratio between the sizes of the diaphragms 1 A'and 3 a transformation of the amplitudes of the oscillations executed advantage obtained by connecting the chamby these diaphragms may be obtained in a known manner. By this means the amplitudes at the diaphragm 3 may be made larger or smaller than those of the diaphragm 1 as desired. When the apparatus is to be used underwater the diaphragm 3 is generally made smaller than the diaphragm l as shown in ,the drawing.

If the diaphragm 1 is attuned to the tone that is to be received, and if the diaphragm 3 is arranged so as not to execute any appreciable oscillations that are due to its own natural period of vibration, a simple, singletone structure will be obtained in which the magnitude of the damping effect due to the radiation of sound energy (radiation damping) is determined at the chosen frequency by the size of the diaphragm 1, and in which the useful damping efl'ect-i e. the amount of damping that produces a useful effect-at a given size of the diaphragm 3 and with a given electromagnet 5, 6 is determined by the coupling action of the chamber 4 and ratio of transformation existing between the surfaces 1 and 3. By enlarging the chamber 4 the useful damping effect is decreased, and by reducing the size of the chamber 4 the useful damping effect is increased. This affords a convenient means of balancing the useful and radiation damping effects. It' the member 3 is also attuned there will be two tuned structures of which, in addition to their inner injurious damping effects, the one embodies the radiation damping effect and the other the useful damping effect. By properly diniensioning the coupling chamber 4 in the manner described above the two vibratory members may then be coupled looser or tighter to each other and a balancing of their damping and tuning effects thus obtained.

Instead of attaching the receiving member proper to the diaphragm 3 another coupling chamber filled with an elastic coupling medium and arranged in accordance with the invention may Ibe interposed between the diaphragm and the said actual receiving member as shewn in Fig. 2. T he various members are then arranged in the following order:

The radiating or sound collecting diaphragm 1 is coupled by means of the coupling chamber 4 to the diaphragm 3.

The diaphragm 3 is in turn coupled by means of the coupling chamber 11 to the receiving device proper 5, 6.

If 1 and 3 were attuned to the tone to be received but not the receiving device 5, 6 it would be possible to change the useful damping of the member 3 by means of the second coupling chamber and the first coupling chamber would enable the closeness of the coupling between the radiating member and member 3 that embodies the useful damping to be altered. Many kinds of such rthe* tigl'itne'ss of the combination groups of chambers or diaphrains may be employed and a numberof individual groups may be arranged one behind the other.

Insteadof flat diaphragins surfaces of any v other shape may be whilst the apparatus is i'nxoperatioii. This device consists of arpiston 13 which. b v means of ai handle 1-1 project-ing from the casing-2, can be' shiftedin the chamber 12 that is connected-'to the coupling chamber 1. The tightness of the coupling' may be altered through shifting the piston 13 from a distance by means of electromagnetically actuated distant control devices` or any other suitable kind of device; The tightness o't' the acoustic coupling vcould of course also be `changed from a` distance by altering the pressure of the air in chamber il.

- The coupling established by the chamber 4 may bealtered duri-ng the operation of the apparatus i-n the vmanner described above or in some other suitable. wav. It the apparatus is 0fa-- kind iii which the coupling `chainber effects a coupling between two structures (diaphragms) which are attuned to execute maximum oscillations at two different frequencies of sound' these structures may be varied b v changing coupling. If the apparatus is such, that its aggregate structure is attuned so asl to execute its maximum oscillations at one certain frequencyy only the variability ofthe coupling effect Will enable relative variationsv ot' the damping effects, viz, the radiation damping and useful damping effects, to be carried out.

In Fig.l 4 a sound vsignaling apparatus is shewn having a coupling chamber, providedV with a coupling medium consisting of a of' gas and liquid. The space between diaphragms 1 andS is filled chiey with a liquid 15 in Which a flat or shallow vessel 16v is immersed l'iaving-Hexible Walls Vand Whose interior 17 is charged'with a (-ible medium,

highly compressible medium or gas. The

rliquid only serves totransfer the motion of diaphragml to thediaphragm 3 and is not compressedto any appreciable extent, Whereas the space 17 in the vessel 16 that is filled with gas acts as an acoustic coupling between the two diaphragms 1 and 3. Vhere a coupling chamber contains both a highly compressible and a substantially incompress- -as in this modification of the invention, the combined effect is as thatr of a compresvsible medium. A similar effect could of coursebe obtained by arranging vibration, the timing of-y v. ai

the gas chamber immediately behindv the i diaphragm- 1, and chamber behind the Figures by disposing the liquid gas chamber. 5 to 7 will also be described as if ythese figures merely represented ,av sub-` merged electromagnetic receiver'. But it must be borne in mind that witlioutany essential alteration the ydescription might be4 taken to refer ljustas Well to a sound producer. 'The coupling chamber in itself is constructed in principle similari)v to lthose in Figs. l to 3 and similar partsare designated by similar signs of reference,l A

In tlie interior ofthe casing 2 of the apparatusshewn' in Fig. 5 an annular cavityy 18 is 'provided which is pling chamber-t by a Wall 19 consisting of a yielding substance that in the preceding description.

Fig. 6v illustrates a modification paratus of Fig. 5 in casing 2 that envelops the chamber 4 is coated with a lining 20co`nsisting of substances which produce'a large amount of friction in their interior.

Iirfth'e modification shewn in Fig.v 7 perforated or sieve-like partitions-2 1 that operate to increase the damping effect` are interposed in the coupling chamber 4 between closed to the conv I servesto increase the? damping effectl for the purpose inentionc'dvj 'f n of the ap- 'which the Wall of thev the diaphragms 1 and 3. The significance of l Y the other -parts will appear from their signs of reference.

In apparatus in which the coupling chani-- bei' has a diaphragm 3 abutting against-it. 100

which is in turn attached to the sound exciting or detecting member 5', G the employment of such members or,v in the case of a sound producer, of ayspeci'a-l exciting niember immediatel)v coupling chamber may leadv to complications in the construction of this kind of apparatus apart .from the general difiiculticsI connected with the use o tivo dial'ihragins, one ot which is the radiating member whilst the other is the suliport that holds the receivingl or exciting device proper, are placed so near to each other as at the boundary of the aii t' special detecting dc- 5 vices, particularly with microphones.y VIVlicn 10 y the purposes of' the in vcntion require, detri- 115 4mental acoustic qualities of the apparatus may also arise through the occurrence of unstable and complicated coupling conditions of tlietwo diaphragins.

In accordance with the invention these difficulties are entirely or partly avoided by arrangements which cause thc coupling` chaniber to affect a second sound conducting chamber, this latter chamber being connected With the former b v an opening which is ot l such size that the coupling effect and at the same time an efficient sound transmission is maintained, In certain instances this opening may be closed .with a r vieldii'ig` diaphragm or plate. f

The second sound conducting chamber just mentioned dill'ers fundamentallw7 from the chamber hereinbet'ore described that is employed for the purpose ot' ell'ecting the closeness of the coupling. The second sound conducting chamber mereljv serves as an eflicient means for conducting. or passing on, the sound waves imparted to the bodlv of gas therein. u ln the simplest form of this arrangement the second chamber may, in the Case of a receivinv apparatus, consist of a pipe leading straight to he ears of the operator. The use, ol' a second diaphragm and a Spccial detecting device is then avoided alto gether. 'the arrangement mayv be such that the said second chamber is in the form of a resonator. A combination of these ar rangements may also be used in which aresonator is interposed between the coujz'iting chamber and the pipe, or between the pipe and the ear.

The contrivanccs mentioned in the last paragraph are intended for the reception ot sound signals h v thc ear. But it altered accordingly.thejr ma)Y also he used for sending out signals. This may be done by connecting an air wave sound producer, which mav be of any lanown type, to the gas chamber which adjoins the coupling chamber. 'l`he 'connection ma)Y be such that the sound producer placed in thc position which, it' the apparatus were used for receiving, would be occupied bjv the ear, and that the sound vibrations emanating` from the sound producer are conducted to the or air chamber and from thence through the coupling chamber to the radiating member. The, sound producer may of course just as well be connected to the air chamber by a special pipe, or itl may be partlyy or eutirel)Y huilt into the said air chan'iber. Special advantages accrue from such arraiueuient in cases where the apparatus` is used tor signaling under water because it @mhh-s- .sourd producers ol' a simpler and cheaper type to he, used and renders it possible to transfer the sound energy produced by thc sound producers to the outside Inedium through which the sound is propagated in an e.\'trcmel \r simple form and jvct at a high etliciency. The sound producers employed might ot course be the organs ot speech so that this arrangement also enable spoken words to be transn'iitted under water between ships, buoys, diving appara tus, etc.

.\n apparatus ot the kind described in the preceding paragraph is shewn for example in Fig. 8 in which the coupling chamber l is connected by an opening or passage Q2, that is so narrowl as not to im pair the coupling effect, a second airchamher Q3 that is cylindrical in form and to which a sound conducting tube 24 is joined that' leads to a sender in the shape of a disk siren. whose disk Q3 is rotated through a shaft Q2 h v a motor Q1 and the interior ot' which is supplied through a lateral pipe 2o with an operating medium under pressure. The end ot the pipe next to the siren is widened in the shape of a conc whose walls" are perforated to allow the operating medium to escape. The size of these perforations is such that the sound waves are not diverted through them.

Fig. t) illustrates a device shaped somewhat ditl'erent from that shown in Fig. 8 but constructed in accordance with the same princij'iles. 'l`he second gas chamber 23 is .wid-.ered out so as to form a speaking trumpet or mouth-piece and the apparatus 2 may be assumed to be'fixed in a suitable spot of l`a divers helmet, a fragment of whose wall 3S is shown. Such apparatus are preierabljv arranged at the two sides of the diver`s helmet at the parts next to the ears, and at the front of the helmet opposite to the divers mouth. To facilitate hearing, special sound conducting tubes may be provided that lead from the chamber f3 to the auditorv ducts ot the direr. In this case the chamber 29; may be shaped as a resonating chamber.

Just as special sound producing devices may take the place of the organs of speech in the examples just described, the place of the ear in a receiving apparatus mav be taken by any suitable form of receiving device. This fact gains in importance in cases where sound waves are to be received which arrive in a medium that is not readily ac cessible to the ear ot the listener and the perception of which is to be carried out in a place to which it may seem objectionable to lav sound conductingl pipes. 4 ln cases like this the sound conductor t'ormed b v the air chambers or ducts ma)r be interrupted at amv desired spot. 'l`he`v may .for example be eut short in the gas chamber itself that adjoins the coupling chamber and a detecting device (such as a microphone, electromagnet, etc., capablel ot' converting the sound vibrations into electrical waves may be arranged in the gas chamber. For conducting the energy thus converted to a place situated bevond the gas chamber and for rendering it perceptible a known means ma)v he employed. A sound signaling apparatus in which an energyv convertiu, l means is arranged in a gas chamber adjoining the coupling chamber shewn in Fig. 10. The paths through which the sound waves are propagated which include t'he outside medium, the diaphragm 1, the coupling chamber -l and the gas chamber 23h, are interrupted at this latter chamber where a detecting device in the shape of a microphone 2G that converts the sound waves into electric waves is arranged in a ring-shaped diaphragm 25 extending across the gas chamber. The electric waves are conducted fromthe microphone by an insulated-electrical' conductor 27 lcd into the gas chamber through a watertight stalling box or gland 28.

If the second gas -chamber behind the coupling chamber is made in they form of a chamber of any general type a mono-resonant apparatus will result,i. e. an apparatus that, as a rule, will possess only one predominant natural rate of vibration, which will be determined partly by the elastic properties of the radiating member and of the abutting coupling chamber, and partly by the mass of the radiating member and of the medium at either side of the radiating member. A system that is on the Whole mono-resonant will also be obtained if the elastic force of, say, the radiating member is made very small and the gas chamber adjacent to the coupling chamber is made to act as a resonator timed to some particular note. By `tuning this gas chamber andthe radiating member Wth respect to each other more or less accurately, and by varying the closeness of tli'e coupling between the said gas chamber and radiatng member, the vibrating system can be made to possess two natural rates of vibration which are more or less near to each other and whose damping, when they are tuned, with respect to eachother, is determined by the sinn of the dampings of the two individualv vibratory elements. By coupling together more than two individual vibratory elements of the kind described it is possible to construct senders or receivers having more than two natural rates of vibration or 'frequencies of resonance. 1

In the apparatus hereinbefore described the area of the radiating member or diaphragm that closes the coupling chamber against the sound propagating medium is preferably'inade relatively large with respect to the area of the diaphragm that is vattached to the detecting or exciting device, or that closes the narrow connecting passage that leads to the second gas chamber or duct, in order to obtain oscillations of large'amplitude at the sound receiving or sending device proper. A similar relation exists be-J tween the area of the radiating member and that of the connecting passage between the coupling chamber and the sound conducting chamber oi' conduit, when the latter form of the invention is employed. It is ,generally necessary, if'a suiiiciently tight coupling is -to be effected with a cone-shaped coupling chamber, to make the coupling chamber exf ytremely flat or shallow'so that it tapers down Very abruptly towards the smaller vibratory body or diaphragm. This results `in the gas contained in the coupling chamber being impelled or oscillated not only in the desired axial direction, i. e. in a direction perpendicular to the radiating diaphragm,

but also in a large measure in a tangential or lateral direction. This latter motion, which, as has already been stated, is by no means always desired, might under certain circumstances even `outweigh the former motion so that the acoustic process becomes extremely complicated and diflicult to estimate. Sincek these undesirable effects are enhanced by the vsaid tangential motfons taking place between surfaces situated extremely close together the damping produced by frictiondue to these motions is frequently so considerable that it is bound to cause grave losses of energy, and this very often just in cases where such losses ought to be entirely avoided or where they are at any rate not permissible to the extent to which they are liable to 0ccur under the aforedescribed circumstances.

But it is not always feasible to ill the coupling chamber with a mixed charge or with a gas having small internal friction, as for example in apparatus in which the cou pling chamber is in direct communication with the sound conducting chamber, conduit or pipe, and therefore a problem requiring solution is to construct the coupling chamber p in such a manner as to avoid the said losses j through friction. The solution presented by adjacentl toI theradiating member, for the" i characteristics of this chamber are then no longer dependent on the size of the radiating member. On the other hand certain limitations on the design of the radiating member having the sameorigin as thosewhich restricted the coupling chamber are removed. Hence the coupling chamber may now be made deeper than it could be in the types of apparatus heretofore described because it is narrower and in this way has the same minute volume.

In reducing this idea to practice the procedure will generally be to attach a rigid member to the radiating diaphragm that projects out from the diaphragm as far as the coupling chamber and forms a wall that y ing of the chamber that faces the said diaphragm in the manner of a piston that closes the said opening. This piston must be of such size that on the one hand there must be a certain amount of clearance between the piston and the wall of the copuling chamber so as to permit the piston to move in unison with the oscillatingradiating diaphragm, but on the other hand this clearance must be so small as to prevent the medium in the coupling chamber from escaping therethrough so freely as to hinder the creation of acoustic pressure fluctuations and vibrations in the coupling chamber.

A greater security against this escape of the air than can be obtained With a simple free piston can be achieved by using some special means for sealing the space between the intermediate member or piston and the periphery or Wall of the coupling chamber. Thus the piston may be connected to the end surface of the coupling chamber by an annular diaphragm which is soft as far as the motions of the piston are concerned but, which is hard in regard to its acoustic properties, inasmuch as its natural freqency of vibration is high.

Apparatus in which the :features described in the last four paragraphs are embodied are shown in Figs. 11 and 12. In the apparatus of Fig. 11 a coupling chamber is'provided opposite to the center of the diaphragm 1 in the form of a cylindrical cavity 4a inthe interior Wall of the casing. A piston 29 rigidly connected to the radiatig diaphragm 1 tits with little clearance into the coupling chamber 4a to which a sound conductor 24 is joined. The sound energy taken up by the diaphragm 1 is transferred by the piston 29 to the coupling chamber 4a. The space 30 in the casing which surrounds the piston 29 is placed in communication with the atmosphere through holes 31 'in order to prevent compressions of the air enclosed in the said space.

The modification illustrated in Fig/12 is essentially similar to the apparatus of Fig. 11 except that the piston 29 is connected to the inner wall of the casing 2 by an annular diaphragm 32 which acts as a seal that completely closes the coupling chamber 4a against the space 8O and which, Whilst being soft and yielding as far as the movements of the piston 29 are concerned, is hard in regard to the oscillations of the air in the coupling chamber.

The connecting member between the coupling chamber and the radiating member, instead of being entirely rigid as in Figs. 11 and 12, may in itself consist of an oscillatory structure which. if desirable, may also be utilized for transforming the amplitudes of the acoustic oscillations. The intermediate or connectig member will be preferably attached to those parts of the radiating member that execute the largest movements when oscillating at the frequency of the sound to be transmitted. This applies particularly to rigid intermediate members, such as for example those shown in Figs. 11 and 12. If it is not absolutely necessary to entirely do away With all the evils residing in flatconical coupling chambers, a sort of combination of a coupling chamber of this kind and of the type j ust described with reference to the Figs. 11 and 12 may be constructed by making a cavity, which may be cylindrical in shape, in the center of the one Wall of the at conical coupling chamber. In an apparatus of this character the said centrally located cavity is situated directly opposite and very near to the middle of the radiating member so that this member itself acts something like a piston, and a special intermediate member between the radiating member and the coupling chamber is unnecessary.

If a special intermediate member is inserted between the radiating member and the coupling chamber the radiating member will `preferably consist of a ribbed, stiened, or piston-like diaphragm. The object of this is to cause the whole of the energy of vibration residing in the radiating member to be transferred to the coupling chamber and to prevent a zone being formed at the point where the intermediate member is attached to the radiating member which behaves more or less like a nodal point.

Apparatus of the kind referred to in the last two paragraphs are shewn in Figs. 13 and 14.

According to Fig. 13 a special vibratory structure 33 is used as an intermediate inember for connecting the coupling chamber 4b to the diaphragm l. The vibratory structure 33 consists of two heads or masses connected byan elastic link member, and may or may not be attuned to a certain tone. The coupling chamber 4b is provided at the end that is farthest from the diaphragm with an adjustable piston-like stopper or seal 34 by which the size of the chamber may be regulated so as to change the degree of coupling. The coupling chamber 4b is connected through a hole 35 in the piston 34 to a sound conducting tube 24. In order to transfer the greatest possible amount ot' the energy of vibration that is taken up by the diaphragm to the oscillatory structure 1 the diaphragm is compelled by stiti'ening ribs 36 (Which only permit fiexui'es of the diaphragm near its periphery and in the space. near the periphery of the mass connected to it) to oscillate in such a manner that no undesirable nodal lines can be formed.

In the apparatus shewn in Fig. 14 the coupling chamber although it abuts against the entire surface of the diaphragm l. is made extremely fiat opposite to the parts of whilst a cylindrical cavity 4C is provided 'Y opposite to the middle diaphragm portion account.

that executes relatively large vibrations, this' cylindrical cavity thus forming thereal coupling chamber or the only effective part of it, whilst the other part maybe left out of In the apparatus shewn in Figsll to 14 the coupling chamber may of course be used similarly as in the previously describedapparatus for transferring energy between the radiating member and the other parts of the apparatus,' not only `in receiving sound signals but also in sending sound signals;

and connections may be made with detecting devices, ete., in the same mannei as hereinf before shown. y

Itis thus seen that the size of the coupling chamber need not be perfectly'unchangeable,

for in accordance with the invention' provision may be made kfor altering its volume. In this way a convenient means of changing the degree of tightnessl ofthe coupling isA produced and at the saine time. the scale of tunableness of the apparatus is made continuous. On account of the elastic properties 0f gases', an elastic power` resides in the contents of the coupling chamber which adds to the elastic force of the adjoining oscillating members.` y The construction of an adjustable coupling chamber is a most simple matter, thev coupling chamber being .prete ablyinade of two parts one of which slides `in the other as in .a telescope;- or Vthe end of the chamber that is farthest away from `the radiating diaphragm being closed by an adjustable piston.` Thispistonpmay, in turn contain a diaphragm or some other form of vibratory member, orv it may comprise a passage leading to a sound conducting tube.

lIn the cases of the apparatus described by yreference to the Figs. 11 and lQ'it was assuine'd ythat only the fundamental vibrations of the` diaphragm wereto be transmitted. But the movablev piston in the coupling' chamber may of course also be coupled with the radiating member in such a manner that the. harmonics yof the diaphragrif, or its fundamental vibrations vandl harmonics standing in a certain relation to eachother, are caused to effect the coupling chamber.

The above described geometrical separa-y tion of the coupling chamber fiom the radiating member is not the onlymeans by which the damping effect/ causedby friction can be reduced, or the invention presents a/second very simple means of accomplishing this, which consists in tuning the `coupling chamber itself to the 'natural frequency of the radiating member, or dia'- phragm. By attuning the diaphragm and, the coupling chamber to each other av closer coupling than thatV which exists between an untuned diaphragm and chamber is obtained in any case. so that for a certain degree of coupling, the coupling chamber may be made larger, which means thatthe damping due to friction can be ina-de smaller. But to obtain an effective acoustic coupling eti'ect between the radiating member and the air chamber the size ofthe latter must still be very small. An evidence of this will be yits peculiar shape, for even if the measures just described are'adopted it will take the form of an extremely iiat or shallow space extendingr across the surface ofthe radiating member. These attuned coupling chambers ywill .also preferably be made conical, although other forms aie possible. To facili- `tate the understanding of the cause ofy this difference in size incase of the coupling chamber being tunedor not tuned, it is necessary lto ima-gine that in a tuned chainber much Wider oscillations of the molecular particles of air are produced by the motion of the radiating diaphragm.V These wider oscillations enhance the variationsof pressure in the air filling of the chamber, especially; in places near the yielding diaphragm or the opening arranged between the coupling fchamber and the connected sound conducting parts or bodies. y

The tuning-ofthe air in the coupling chamber enables this latter to be made larger, so .that it may for example in some cases be made ten times larger than before, without diminishing the closenessof coupling.`

If the radiating member and coupling gas i ico chamber are both attuned as described the sound signaling apparatus will have two maxima. ofresponsiveness or frequencies of resonance corresponding to two different Wave lengths and care must be taken that in sending out or' receiving a certain tone.-as in signaling, one of these wavelengths or frequencies corresponds to that of this tone, i. e. the signaling tone. If twodifferent ones are to be sent out or received the two vibratber-may be so timed and the tightness of Vtheir coupling made such that the two favorl able frequencies i. e. the frequencies of resonance at which the best effects' are obtained, are those/of the said tones. Under certain lng systems-radiating member and cham.

circumstances it will be advantageous for..

v'the reception of a certain tone orv group of of coupling'then chosen will prefer/ably be such that the signaling frequency lies in the depression, care being taken that this depression does not sink very far below the two crests in the resonance curve.

Apart from the fact that by tuning the gas coupling chamber (resonator) with re spect to the diaphragm the coupling obtained between them is better in any case than if they were not tuned, the tightness of the coupling itself may here again be adjusted by the size and especially by the height of thechamber. The smaller, i. e. lower or shallower the resonant coupling chamber is made7 the tighter its coupling with the diaphragm will be. By constructing the resonant chamber so that its size may be varied, the tightness of the coupling is rendered adjustable during the operation of the appa ratus.

If the sound energy is to be conducted from or to the coupling chamber b v means of a body of lair, this can be conveniently done by connecting the chamber with the body of air through an opening or passage of a certain size. In doing this it must be borne'in mind that for a `given sound pitch each size of the resonant chamber requires a certain corresponding size of the said passage, and assuming the sound pitch to be constant the size of .the passage or opening decreases as the volume of the chamber is diminished or as the resonant chamber is made lower or more shallow.

An apparatus of the type foreslmdowed in the precedingveight paragraphs is illustrated in Fig. 15A-,which represents an apparatus with a coupling chamber attuned to the radiating diaphragm, the tuning feature being made evident by the relative size of the coupling chamber being shewn todill'er from that of the coupling chambers that are not tuned. l again indicates the diaphragm that serves as a radiating member that closes the casing 2 that envelops the tunable coupling chamber or resonant chamber 4. This chamber is bounded at the opposite side, by another diaphragm B7 in which vthere is an opening Q2 that allows the sound waves to pass into the sound conductingl tube 24.

Fig. 16 represents a resonance. curve of an attuned apparatus of the kind shewn in Fig. l5. this curve representing the values obtained if the apparatus is made to act as a sound receiver and is excited by sound waves with a gradually increasing number of vibrations per second. The abscissas represents the frequencies of vibration of the sound that excites the apparatus and the ordinates show the corresponding loudnesses ]nrceived. The frequency employed for signaling is n. The radiating member and the resonant coupling chamber are attuned to the frequency n and the tightness ofthe coupling chosen is such that the depression s between the two crests that represent the conditions for complete lresonance does not sink very much below the crests.

By this means the range of frequencies within -which a satisfactory loudness or responsiveness is obtained with the apparatus is considerably extended. By increasing the damping ell'ect it is of course possible to extend this range at will at the cost of loudness. This would be done in cases where the sounds from a .plurality of sound producers whose frequencies differ are to be received by one and the same receiving apparatus, or

where trains of tones are to be received or sent out which contain different individual .tones as in detecting noises or in telephon mg.

In conducting sound energy by means of a body of air from or to the coupling chamber it might happen that the sound conductor produces a detrimental reaction upon the part of the sound signaling apparatus that comprises the diaphragm and coupling chamber inasmuch as it causes changes of the tuning and damping of this part. This disturbing reactive influence makes itself felt particularly when the coupling chamber is attuned to the diaphragm. Every change of the sound conducting pipe then gives rise to a variation"y in the conditions of tuning.

In accordance with the invention it is also possible to avoid this disadvantage and this is done by leaving a freer space between the sound conducting pipe and the resonant Coupling chamber.

If a plurality of sound transferring chambers are arranged one behind the other. say for example a separate resonator is placed behind the coupling chamber. then the free space must be interposed between those parts of the path along which the sound travels whose tuning is to remain constant and the parts of this path whose function is simply that of conducting the sounds.

In order to preserve the mechanical continuity of the apparatus the intermediate free space or break in the' structure, is bridged over and enclosed by a cover that is arranged at a considerable distance from the break and that also serves to prevent dirt etc. from penetratingr into the interior of the apparatus. A form of apparatus having this feature is illustrated in Fig.. 17. In this embodiment of the invention the coupling chamber 4 in the sound box 2. which latter is closed at one end by the diaphragm l, is in communication through an opening 22 in the rear wall 37 with the sound conducting pipe 24. The pipe or tube 2% is provided with an extension member 43 forming a portion thereof which flares outwardly towards its end facing the opening or sound passage Q2. This extension member 43 is provide-d with an annular shoulder or flange by means of which it 'is secured to .the body or box, thus fixing the conduit 24 in properrelation to the passage provided withth'e meansjlQflSand 1415erl altering-.the volume ofcoupling chamber- `rfand also-the normal pressure -lth'erf in',l as' -ali 2 r.eady'described-,withreference to Figure 3; i and-also v'with thefthrottling:arrangement 8`,

' A9 'and 19;? as already# ence to vFign--refl-..,`. c, ,y g 'v 1 f ,The improved'l-,ei' iency,' of s oun d-` boXes` not .providedfwith special detecting devices, resulting vfrom J the yHiVIlton,r enables,l them"V f to befnovvgused'l for practical: purposes Zon' board ship; They'. may bef-arranged inra,Y ii l"known (manner. 'with-their 'sound receiving-f Vor lemitting 'diaphragml situated v.ina perl foration of thef's'hips lilull,`or' inside a tank-f orvessel (or on the-,'wallgof such a vessel),v

'containing ,a liquid andV arranged .on thezinl v ner surface -of the ships skin". .The'latteri 22. v:At 42 there is a freeispacejor interspaoe between theV rear vexteri or= wall "of thefcou-v v plingfcliamber 4 andthe sound conducting `;'pipe V24, th'isiinterspace preventing as stated hereinbeforea .reaction of the 'pipe 2401i." the chamber 4 through thefo'peningQQ. The

yannularjshoulder o r angeonthe extension f memberl serves tolofridgev over the -reev '1 -space' or )break .42 and4 seal the against outsideinl`u enoes'. V

' The embodiment V,shown "in thisV figure is deeibedwrhrefaarrangement has hithertdeen iinpo'ssibleon; account of the p o'o'r; eiiclency goffthe sound ging'in-'the shi the fitting vo 'fratus into the Y' 'ship'v will arise inasmuch asv itf,Willfbevr necessary to frivet orfweld theV Yradiating mei'nberforl diaphragm, e. atv Jleast'one part of the-apparatusgto the wall fyof the l:shipV during its construction Whilst' it will generally not ybe,possible to havefthef other parts of theapparat'us also ilrnine'diatefV .ly'istalled by the Ship'builderf'This gives `riseftotwo great disadvantages: In thel first f placethe. operationsv-suchas' welding' or* riveting necessary to. -l'xafthe diaphragm fin y f -place are'fliable to seriouslyalter tu'ni ingg and then it is dillicult or impossible" if, fas is usually the vease,` the other parts are "built inat a'much. later period andby a different, supplier, to properlyV fit thelparts together. Tor removeV al1 "these, drawbacks' boxes in t question" `and becanse@V of lith-eY loss* of energy Voccurri 1 4in thezpassag'e, of; the@ lsoundthrough the ifs ipswvall.; l

f Y But if the apparatus i's :placediin an opens Wall orhully a'idliiculty in` the sound signaling appa# ris another fof the'fOb-jc'ts of this invention 1y and this isfaccomplished by dividingjthe sound signa-ling systemjnto tvvo fundamenf ftally-di'erent parta-:a: pure:ship-building i part and vthe; :sound signaling apparatus, I 'POPG thtform'er of vvhich"is yput in durvnsft-ruojt-ionoftheship -intheship-V "d4-Whilstfthe'latter js tiXedL-in wreef-firmer -faranyr-1ater interior Qing apparatus is?, nc'itfplaceiii immediately byV the expert constructors of the sound sigvi Y naling*apparatug,According to theIinven.-i tion-the formerpartA` isV constructed -in` Ythe 1 form 'of a Water lnlet-With a'fmovableclosfing'member-or Watergate and a device for 70V ymounting the' lsoundsignaliiig,apparatus-be hind the gate. An ordinary slide valve'fand lia-ngc may abe usedfor thisv purposef The@ lconstruction'of the soun'dfboxisv siichthatV 'wlie'nthe,closingfmemberis opened andthe water en'tersinto lcontact Withits r1a 'cli atir1g memberfthe'latter'closesup'ihe openingin,.v thehullf 'Y In comparison with@ known e 'devices of similar character, Whiehjhave allfbeen built '8, so as, toenablethe sound Signaling apparai L tus tofbe'protruded through thehull and toV be drawn backY through it,f' thefdistinguish Y ling feature of the new devicey consists in the rfsond'box beiing arranged ,in aiixedposition "35, and'in the `water gate "not being used, as' an g auriiiary member -requiringf frequent na- 'iiipulaton'by'an operator but'nierelyms a 'rneans-'for'enablingthesmmd s ignalingaapV f Y, 'paiatusV to befinstalledfin strictcornpliance 9- V Withthe VeXisting"acousticconditions. Fig.1181:representsaniarrangeinent 'whichv 'fa soundV signaling apfiaratu's con` structed-iii'- accordance with"gthefinventionis; inserted in en @peeing inthe hause; ernste "casingl of 'the apparat-us', is pifovided?Within Y j 'flange 39 which; abuts against thefbordei" thesai openingsofa's tofiorm awaterti According against theopening inthe hull, but in order ,to enable'it to b e installed.at a'1iy'jtiine itiis,"` T .combinedwith an'independentvvater gate '5115' that iseqipped -witha slide'j valve;`52fandf105f Vwhich has been previously liked bythev ship, builder to the hull 38`by-rivets orf'ther means.k 'The soundsignaling apparatus is@ fixed by yflauiges. 54. Inzlfig. 19 the, difa5 tphragmis almost flush with'th ,fanges5butgfllm- Y t according* to Fig; 20 `fthe" arrangementi's suchVV that'thejdiaphragrn approaches as nearjfa Vpossiblefto the slide valve 52 so'as'tofavoid lossesand directive inluencesthatmightjocfcurA through the Vsound *having to a ss`` l throughfthe channel ofthe Watergate. isf arrangement may ot course-fbeusedjforall 7; i forms `ofsouiid :boxes made fin' accordance with the inventan-'this being indicarme zo this reason the casing of the sound signaling apparatus is provided with a neck 41 to the rear end of which a flange 39 is joined that is riveted to the wall of the tank in the manner illustrated in Figs. 18 and 21. Sound signaling devices of this kind may be used for transmitting sound between ditt'erent mediums as between Water and air, and also between similar mediums, as from air to air. But they mayalso be used for converting electrical or `mechanical energy into sound energy or vice versa, as by causing the diaphragm to be oscillated by an electro magnet instead of using it as as a receiving member actuated by the vibrations ofa sound conducting medium.

In Fig. 23 an apparatus is shown in which most ofthe principal features of the invention are applied. Fixed to the interior of the hull 38 of a ship or buoy is a tank 40. Fitted into an opening ,in the back Wall ot the tank is a sound signal receiver that is fixed by `means of flanges 39. The. dia phragm 1 of receiver is providedv with ribs 36 and abuts against the'liquid charge in the tank. Arranged in liquid at the right of the diaphragm 1 is an air coupling chamber 17 in the shape of a very flat or shallow shell. This chamber is connected by air passages with the space 12, by which the gas pressure in the coupling chamber may be varied, and with the auxiliary chamber 30 into which the air is diverted from the coupling chamber when sounds of a low` rate of vibration are received. The piston 13 is pushed into 12 by its handle 14 when the pressure in 17 is to be raised. The screw inl 9is for establishing or cutting off communication be-V tween the coupling chamber and the auxiliary chamber or for regulating the throttling eiect of the passage through 8.

The space filled with liquid 15 and the air i vessel 17 is closed at the right by a diaphragm 3 that is smaller than the diaphragm 1, so that 3 executes much larger vibrations than 1. The diaphragm 3 is attached to a vibratory structure 33 consisting of two masses connected by a longitudinally elastic rod, the right hand mass of which affects a second coupling chamber 4; that is only made very small and which is in turn functionally connected through a diaphragm 37 and a small hole or passage 35 in v37 to an air chamber 23 which may be taken to represent the beginning ot the actual sound conducting channel or pipe. The opening 35 is not present, i. e. is closed. in cases Wherethe chamber 4a is charged with a medium nuclei' Instead of-using the diaphragm 37 the operative connection between the chambers 1-a and 29 could be obtained through a simple opening or passage of sutlicient smallness. An increase of damping effect, which is necessary in cases Where the i. e. Where the tuning ,is too sharp, may 'be obtained by means of perforated damping;Y Walls or grids 21 with staggered holes and by lateral damping Walls 19. rl`he clearance that is necessary between' the right hand mass of vibratory structure 33 and the walls of the chamber 4 to enable the mass to vibrate freely, is closed by an annular 4seal 32 made of a suitable yielding substance, so as to prevent the air from streaming to and fro between la and 30,"because this would preclude the production ot' suiciently large amplitudes of pressure i114". Adjoining the chamber V23 is a Helmholtz resonator 23 tuned to the frequency of thesignaling tone, and from the resonator` a sound conducting tube 24 passes on tothe operators or listoners station., I

, Between the sound signaling 4apparatus itself-of which in this case the resonator forms a Vpart-fand the sound conductor 24 a small free interspace or gap42 is interposed for the purpose of reducing the deleteriousl reaction of the sound conductor on the tuning of the resonator. To prevent foreign substances from getting into the-gap this latter is protected by ,a guard L11.

The apparatus operates as followszl'lhe Y sound Waves arriving from Without impinge against the hull 38 and are passed on by the water in the tank 40 to the diaphragm 1 which is caused to execute vibrations Whose amplitude is approximately that of the vi-v brating molecules of Water. On account of the smallness of the chamber 17 the fluctuations of the pressure of its contents are very large and these are passed on by the surrounding liquidl to 3 and'thence to 33. I

'motion, and this motion is propagated in the sound conductor24. The distribution of the masses in 33 may be such (right hand mass smaller than the left) that this structure 33 also assists in increasing the amplitudes ot the oscillations as they pass on toward 4.

By tuning the individual diaphragmsythe air chambers, and the vibratory structure u'ith respect to each other and to the signaling frequency a very considerable further improvement of the receiving' properties o1. the apparatus iu regard to loudness and reduction of disturbing effects can be obtained, as has already been hereinbcfore specifically explained.

To meet the practical requirements on board ship a plurality of soundsignaling devices is needed of which for certain purposes, such as'iinding the direction of a( 

